Liquid crystals are generally classified into low and high molecular weight liquid crystals. The low molecular weight liquid crystals characterized by very quick response are currently used in display elements or the like, but are difficult to form large surface area elements because of processing difficulty.
On the other hand, the high molecular weight liquid crystals include high molecular weight compounds having a mesogen group bonded to their backbone and compounds having a mesogen group grafted to a side chain, and the latter side chain type compounds are known to have useful characteristics as display elements. These compounds having a mesogen group on a side chain can have a backbone selected from a variety of chains while compounds having a siloxane backbone have superior temperature properties and weather resistance among others. For example, Japanese Patent Application Kokai No. 234086/1988 discloses thermally stable, weather resistant siloxane compounds which can be manufactured in film or sheet form having a large surface area.
Siloxane type liquid crystalline compounds, however, have the drawback of low response speed though acceptable for use as lighting control glass or the like. This is because these high molecular weight liquid crystals are too viscous at room temperature to drive by the conventional liquid crystal cell driving method. Therefore, these liquid crystals must be placed in a constant temperature tank or heated by a dryer or heater before they can be driven.
Further, dye-modified liquid crystals having polyacrylate and polymethacrylate backbones are known from European Patent No. 90282. Liquid crystalline copolymers having a siloxane backbone are also known from Japanese Patent Application Kokai No. 77910/1988 disclosing liquid crystalline copolymers containing an anthraquinone dye. Although the liquid crystalline copolymers are described as useful in information storage, no reference is made to a mechanism or process of recording information or providing memory. The only description found therein is that the liquid crystalline copolymers are colored with the dyes and effective as auxiliary substances for dissolving dyes in a guest-host manner.
Additionally, Japanese Patent Application Kokai No. 282269/1989 discloses silicone liquid crystals containing azo dyes while a mesogen group is not specified. A general description indicating the potential use as information recording material is found, but memory ability is referred to nowhere in Examples and the specification. Dyes are described as simply imparting color.
In summary, no references have specifically described the memory ability of liquid crystal.